The present invention concerns a transmission for an extruder with two tapering helical shafts.
A transmission of this genus is known from European Published Application 275 485. The shafts rotate in opposite senses and are connected to take-off shafts. A cogwheel is mounted on each take-off shaft. The cogwheels engage each other and distribute the force. Since the shafts slope toward each other, the cogwheels must be conical. Conical cogwheels, however, are more complicated and costly to manufacture than straight cogwheels. To ensure precise meshing of the extruder's threads, the cogwheel teeth must be precisely dimensioned to eliminate the need for expensive regrinding. They cannot be allowed to slip back and forth radially on the take-off shaft. The situation becomes even more complicated when both helical shafts are intended to rotate in the same sense and a third conical cogwheel is accordingly mounted between the other two.
Rotationally rigid compensating couplings (Taschenbuch fur den Maschinenbau, Dubbel, 14th ed., 1981, 409) are generally employed when precisely angled transmission is necessary or when shafts are subject to errors in radial or angular alignment or to axial displacement. Cardan shafts and shafts with engaging cogs are examples.
An extruder with two parallel helical shafts is known from German OS 4 129 913. The transmission that distributes the force from the take-off shaft is separated from the processing section, which accommodates the helical shafts. The force that drives the latter is derived from the transmission by way of cardan shafts. This approach is intended to allow the transmission design to be independent of the narrow gap between the parallel helical shafts.